Re: A problem with g++ compiler

=?ISO-8859-1?Q?Daniel_Kr=FCgler?= <>
Tue, 2 Nov 2010 04:01:22 CST
On 02.11.2010 02:18, luca wrote:

suppose we have the following structure:

typedef struct mystruct_t
int v1, v2;
unsigned char *v3;

// constructor
mystruct_t( int p_v1, int p_v2, unsigned char *p_v3) : v1(p_v1),
v2(p_v2), v3(p_v3)
} mystruct_t;

and the following class:

class MyClass
static myfunc(mystruct_t&m);

Somewhere in my code i have the following line:

// ..
MyClass::myfunc(mystruct_t(1, 2, NULL));

It compile with Visual C/C++ , but when i try to compile it with g++
(using linux Mandriva + Eclipse IDE), i get the following error:

no matching function for call to 'MyClass::myfunc(mystruct_t&) '

I can't really understand why g++ can't compile that line. I simply
construct on-the-fly a mystruct_t object and pass it to myfunc()
static method...

Any idea?

This is one of the most persistent non-conformity examples of the
MS compiler families. The code is ill-formed, because an attempt is done
to bind an rvalue (the temporary produced from the expression
mystruct_t(1, 2, NULL)) to an lvalue-reference to non-const. Every
compiler has to reject this code when compiling in conforming mode.
Disable the Compiler "extensions" (/Za) of the Visual Studio compiler
and you should recognize that it will be rejected as well. This is one
of the examples how long-reaching effects pre-standard rules can have on
todays compilers.

Among the hundreds of discussions of this situation you might find the
following one helpful:

Solutions: If you do not intent to modify the argument within myfunc,
use the parameter type 'const mystruct_t&', otherwise create a normal
variable and provide the corresponding lvalue to the function. From
C++0x on an alternative solution would be to use an rvalue-reference as
parameter type.

Interestingly this question is not part of the FAQ (or I could not
find it). The nearest one I found was:

HTH & Greetings from Bremen,

Daniel Kr?gler

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